especially those of us who fly the longer legged beasts, where 4 hour
enroute
...
It's easy to get really sleepy at 11 000 feet at night,

11 000 ft at night for 4 hours is a situation where a pilot should
definitely use oxygen, regardless the legal situation.

Stefan

My first instinct is to say (and I do believe) it depends on the pilot's
condition, but there's little doubt using O2 about 10,000 feet is usually a
good idea.

Sure makes sipping a martini difficult, though.

AJW